Highly Conductive Ferroelectric Cellulose Composite Papers for Efficient Triboelectric Nanogenerators

Paper‐based electronics has attracted growing interest owing to many advantages of papers including low‐cost, abundance, flexibility, biocompatibility, and environmental friendliness. Despite recent progress in paper electronics, however, development of a high‐performance paper‐based triboelectric nanogenerator (TENG), which is a power‐generating device that converts mechanical energy into electric energy by coupling triboelectrification and electrostatic induction, remains a challenge mainly due to weak electron‐donating tendency of cellulose‐based papers. In this work, highly conductive ferroelectric cellulose composite papers containing silver nanowires and BaTiO₃ nanoparticles are fabricated, and their successful application for realizing a large‐area TENG with enhanced electrical output performance is demonstrated. It is found that triboelectric charge generation on the ferroelectric cellulose composite paper can be promoted by simple poling treatment, which significantly enhances TENG performance. The ferroelectric cellulose composite paper–based TENG exhibits an electrical output performance that surpasses those of aluminum‐based and pristine cellulose–based TENGs by more than two times, as well as outstanding output stability without a noticeable degradation in performance during 10 000 cycles of a repeated pushing test. The work demonstrates the great potential of multifunctional cellulose‐based papers for TENG and other self‐powered electronic applications.     

Cellulose II Aerogel‐Based Triboelectric Nanogenerator

Cellulose‐based triboelectric nanogenerators (TENGs) have gained increasing attention. In this study, a novel method is demonstrated to synthesize cellulose‐based aerogels and such aerogels are used to fabricate TENGs that can serve as mechanical energy harvesters and self‐powered sensors. The cellulose II aerogel is fabricated via a dissolution–regeneration process in a green inorganic molten salt hydrate solvent (lithium bromide trihydrate), where. The as‐fabricated cellulose II aerogel exhibits an interconnected open‐pore 3D network structure, higher degree of flexibility, high porosity, and a high surface area of 221.3 m² g^?1. Given its architectural merits, the cellulose II aerogel‐based TENG presents an excellent mechanical response sensitivity and high electrical output performance. By blending with other natural polysaccharides, i.e., chitosan and alginic acid, electron‐donating and electron‐withdrawing groups are introduced into the composite cellulose II aerogels, which significantly improves the triboelectric performance of the TENG. The cellulose II aerogel‐based TENG is demonstrated to light up light‐emitting diodes, charge commercial capacitors, power a calculator, and monitor human motions. This study demonstrates the facile fabrication of cellulose II aerogel and its application in TENG, which leads to a high‐performance and eco‐friendly energy harvesting and self‐powered system.     

Highly Porous Polymer Aerogel Film‐Based Triboelectric Nanogenerators

A novel class of high performance polymer porous aerogel film‐based triboelectric nanogenerators (A‐NGs) is demonstrated. The A‐NGs, made of a pair of highly porous polymer films, exhibit much higher triboelectric outputs than the corresponding dense polymer film‐based triboelectric nanogenerators (D‐NGs) under the same mechanical stress. The triboelectric outputs of the A‐NGs increase significantly with increasing porosity, which can be attributed to the increase in contact area and the electrostatic induction in the porous structure, thereby leading to additional charges on the porous surface. Remarkably, the A‐NG fabricated using porous chitosan aerogel film paired with the most porous polyimide (with a porosity of 92%) aerogel film demonstrates a very high voltage of 60.6 V and current of 7.7 µA, corresponding to a power density of 2.33 W m^?2, which is sufficient to power 22 blue light‐emitting‐diodes (LEDs). This is the first report on triboelectric nanogenerators (TENGs) employing porous polymer aerogel films as both positive and negative materials to enhance triboelectric outputs. Furthermore, enhancing the tribopositive polarity of the cellulose aerogel film via silanization using aminosilane can dramatically improve the triboelectric performance. Therefore, this study provides new insights into investigating porous materials with tunable triboelectric polarities for high performance TENGs.     

Advances in Triboelectric Nanogenerators for Self-Powered Regenerative Medicine

Over the last decade, in pursuit to provide suitable alternatives for power supplies of medical devices in regenerative medicine, extensive research on nanogenerators has been developed. Such devices can overcome current commercial battery challenges, including intense heat-on-body complications due to the electrical current during therapeutic usage, leading to protein denaturation, cell structure destruction, and even cell necrosis. In addition, these traditional batteries contain a bulky and heavy structure that prevents them from providing sustainable on body biomedical therapeutic intervention. Furthermore, advantages such as wide-range biocompatible and biodegradable materials, lightweight, and sufficient stretchability for device construction can minimize the side effects of implantable devices, including inflammation or toxicity, as well as eliminate secondary surgery to replace or remove batteries. Triboelectric nanogenerators (TENGs) are associated with harvesting mechanical energy in various forms, among which human body motions can serve as a renewable power source for healthcare systems. This review is written to emphasize the importance of TENG's applications in regenerative medicine and modulation purposes, particularly for the nervous system. Some crucial parameters for implantable consideration are discussed. In the concluding remarks, features for clinical utilization including output efficiency, encapsulation, stability, and miniaturization are suggested as challenges and prospects.     

Dielectric Modulated Glass Fiber Fabric-Based Single Electrode Triboelectric Nanogenerator for Efficient Biomechanical Energy Harvesting

Single-electrode triboelectric nanogenerators (SE-TENGs) are versatile tools for energy harvesting with simple structures and great practicability. However, low output performance hinders SE-TENGs in applications as portable power sources. Herein, a novel SE-TENG that utilizes glass fiber fabric (GFF) as tribo-materials, along with an inorganic ferroelectric film for the dielectric layer is proposed. The GFF is first shown to be a promising tribo-material for its highly positive tribo-polarity and unique chemical/mechanical/durable properties. Meanwhile, an inorganic dielectric film with high dielectric constant is introduced between the GFF and Al electrode for enhancing the charge trapping capability. Owing to the synergistic effect of optimized triboelectrification and dielectric properties, the specific designed SE-TENG delivers an open-circuit voltage of 1640 V and a short-circuit current density of 59.05 mA m⁻², which are superior to most reported SE-TENGs. With a maximum instantaneous power of 11.30 mW, the device can light up 1350 light-emitting diodes, charge a 47 µF capacitor into 10 V in 421 s, and power up a digital watch even without additional control circuits. This work provides new insights in designing high-performance SE-TENGs and facilitates their application in biomechanical energy harvesting and portable power sources.     

Bioinspired Triboelectric Nanogenerators as Self‐Powered Electronic Skin for Robotic Tactile Sensing

Electronic skin (e‐skin) has been under the spotlight due to great potential for applications in robotics, human–machine interfaces, and healthcare. Meanwhile, triboelectric nanogenerators (TENGs) have been emerging as an effective approach to realize self‐powered e‐skin sensors. In this work, bioinspired TENGs as self‐powered e‐skin sensors are developed and their applications for robotic tactile sensing are also demonstrated. Through the facile replication of the surface morphology of natural plants, the interlocking microstructures are generated on tribo‐layers to enhance triboelectric effects. Along with the adoption of polytetrafluoroethylene (PTFE) tinny burrs on the microstructured tribo‐surface, the sensitivity for pressure measurement is boosted with a 14‐fold increase. The tactile sensing capability of the TENG e‐skin sensors are demonstrated through the characterizations of handshaking pressure and bending angles of each finger of a bionic hand during handshaking with human. The TENG e‐skin sensors can also be utilized for tactile object recognition to measure surface roughness and discern hardness. The facile fabrication scheme of the self‐powered TENG e‐skin sensors enables their great potential for applications in robotic dexterous manipulation, prosthetics, human–machine interfaces, etc.     

Rolling Friction Enhanced Free‐Standing Triboelectric Nanogenerators and their Applications in Self‐Powered Electrochemical Recovery Systems

Heavy metals contained in wastewater are one of the most serious pollutions in natural resources. A self‐powered electrochemical recovery system for collecting Cu ions in wastewater by incorporating a rolling friction enhanced freestanding triboelectric nanogenerator (RF‐TENG) is developed here. The RF‐TENG utilizes integrated cylindrical surfaces using the conjunction of rolling electrification and freestanding electrostatic induction, which shows outstanding output performance and ultrarobust stability. By using the kinetic energy of flowing water, a collection efficiency of up to 80% for Cu²⁺ ions in wastewater has been achieved. Self‐powered electrochemical systems are one of the most promising applications of TENGs for independent and sustainable driving of electrochemical reactions without the need for any additional power supply. This research is a substantial advancement towards the practical applications of triboelectric nanogenerators and self‐powered electrochemical systems.     

Robust Solid-Liquid Triboelectric Nanogenerators: Mechanisms,Strategies and Applications

Solid-liquid triboelectric nanogenerators (SL-TENGs) are a new technology that combines contact electrification (CE) and electrostatic induction to collect clean energy stored in natural water. Considering their unique advantages of high energy density, wide selection of materials and being suitable for large-scale promotion, they have attracted more and more attention in recent years, and numerous studies have shown their great potential in various applications. Many critical applications of SL-TENGs inevitably involve sustained and stable high electrical output. To achieve stable output performance and long cycle life in these applications, the adaptability of SL-TENGs to material selection, structural design, and working environment is necessary. Therefore, the construction of SL-TENGs matching different applications has become a critical research direction in TENGs. This review provides a historical summary of the development of SL-TENGs in the past few years and analyzes the key factors affecting their electrical output performance. The exciting achievements of different constructions of SL-TENGs for practical applications is also demonstrated such as energy harvesting, self-powered sensing, and self-powered cathodic protection. Finally, the development prospects of SL-TENGs and the significant challenges for their further development is discussed.     

Ferroelectric‐Polymer‐Enabled Contactless Electric Power Generation in Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) are considered as one of the most important renewable power sources for mobile electronic devices and various sensors in the Internet of Things era. However, their performance should inherently be degraded by the wearing of contact surfaces after long‐term use. Here, a ferroelectric polymer is shown to enable TENGs to generate considerable electricity without contact. Ferroelectric‐polymer‐embedded TENG (FE‐TENG) consists of indium tin oxide (ITO) electrodes, a polydimethylsiloxane (PDMS) elastomer, and a poly(vinylidene fluoride) (PVDF) polymer. In contrast to down‐ and non‐polarization, up‐polarized PVDF causes significantly large triboelectric charge, rapidly saturated voltage/current, and considerable remaining charge due to the modulated surface potential and increased capacitance. The remained triboelectric charges flow by just approaching/receding the ITO electrode to/from the PDMS without contact, which is sufficient to power light‐emitting diodes and liquid crystal displays. Additionally, the FE‐TENG can charge an Li‐battery with a significantly reduced number of contact cycles. Furthermore, an arch‐shaped FE‐TENG is demonstrated to operate a wireless temperature sensor network by scavenging the irregular and random vibrations of water waves. This work provides an innovative and simple method to increase conversion efficiency and lifetime of TENGs; which widens the applications of TENG to inaccessible areas like the ocean.     

Theoretical Investigation and Structural Optimization of Single‐Electrode Triboelectric Nanogenerators

Single‐electrode triboelectric nanogenerators (SETENGs) significantly expand the application of triboelectric nanogenerators in various circumstances, such as touch‐pad technologies. In this work, a theoretical model of SETENGs is presented with in‐depth interpretation and analysis of their working principle. Electrostatic shield effect from the primary electrode is the main consideration in the design of such SETENGs. On the basis of this analysis, the impacts of two important structural parameters, that is, the electrode gap distance and the area size, on the output performance are theoretically investigated. An optimized electrode gap distance and an optimized area size are observed to provide a maximum transit output power. Parallel connection of multiple SETENGs with micro‐scale size and relatively larger spacing should be utilized as the scaling‐up strategy. The discussion of the basic working principle and the influence of structural parameters on the whole performance of the device can serve as an important guidance for rational design of the device structure towards the optimum output in specific applications.     

High‐Performance Triboelectric Nanogenerators Based on Electrospun Polyvinylidene Fluoride–Silver Nanowire Composite Nanofibers

The preparation of ferroelectric polymer–metallic nanowire composite nanofiber triboelectric layers is described for use in high‐performance triboelectric nanogenerators (TENGs). The electrospun polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite and nylon nanofibers are utilized in the TENGs as the top and bottom triboelectric layers, respectively. The electrospinning process facilitates uniaxial stretching of the polymer chains, which enhances the formation of the highly oriented crystalline β‐phase that forms the most polar crystalline phase of PVDF. The addition of AgNWs further promotes the β‐phase crystal formation by introducing electrostatic interactions between the surface charges of the nanowires and the dipoles of the PVDF chains. The extent of β‐phase formation and the resulting variations in the surface charge potential upon the addition of nanowires are systematically analyzed using X‐ray diffraction (XRD) and Kelvin probe force microscopy techniques. The ability of trapping the induced tribocharges increases upon the addition of nanowires to the PVDF matrix. The enhanced surface charge potential and the charge trapping capabilities of the PVDF–AgNW composite nanofibers significantly enhance the TENG output performances. Finally, the mechanical stability of the electrospun nanofibers is dramatically enhanced while maintaining the TENG performances by applying thermal welding near the melting temperature of PVDF.     

Self-Powered Syringe Pump for Insulin Pump Therapy Based on High-Voltage Triboelectric Nanogenerator and Dielectric Elastomer Actuator

Insulin pump therapy (IPT) is commonly utilized for treating type 1 diabetes. However, the insulin pump is generally rigid, and its prolonged use can cause discomfort to patients. Additionally, the device suffers from other drawbacks such as limited battery life. Herein, an IPT system consisting of a dielectric elastomer-based soft syringe pump (DE-SSP) and a high-voltage triboelectric nanogenerator (H-TENG) is introduced, which can achieve stable and adjustable liquid output depending on real-time blood glucose. The maximum pump volume of this IPT can reach 262.4 or 303.7 µL when powered by a DC source or H-TENG, respectively, which is generally sufficient to meet the requirements of the therapy. H-TENG possesses a sensitive self-protection mechanism that minimizes the risk of electrical damage and it can be easily fabricated or repaired and flexibly designed according to the application environment. The proposed IPT system is compatible with different placement angles and utilizes compliant electrodes with good biocompatibility that ensure its safety. It also overcomes common issues including rigidness, relatively fixed bolus delivery options, and short battery life associated with traditional insulin pumps. This study not only demonstrates a combination of H-TENG and DE-based actuators but also opens new avenues for microelectromechanical systems micropumps.     

Fully Elastic and Metal‐Free Tactile Sensors for Detecting both Normal and Tangential Forces Based on Triboelectric Nanogenerators

A tactile sensor should be able to detect both normal and tangential forces, which is mandatory for simulating human hands, but this fundamental function has been overlooked by most of the previous studies. Here, based on a triboelectric nanogenerator (TENG) with single‐electrode mode, the fully elastic and metal‐free tactile sensor that can detect both normal and tangential forces is proposed. With tiny burr arrays on the contact interface to facilitate the elastic deformation, the detected normal pressure by the device can reach to 1.5 MPa with a sensitivity of about 51.43 kPa V⁻¹, and a large range of tangential forces can be detected ranging from 0.5 to 40 N with rough sensitivity of 0.83 N V⁻¹ (0.5–3 N) and 2.50 N V⁻¹ (3–40 N). Meanwhile, the applied tangential forces from different directions can also be clearly distinguished by the four‐partitioned electrode structure. Moreover, a shield film is coated on the top surface of the device, which can screen the electrostatic interference and enhance the repeatability of the device. The demonstrated concept of this self‐powered tactile sensor has excellent applicability for industrial robotics, human–machine interactions, artificial intelligence, etc.     

All‐Plastic‐Materials Based Self‐Charging Power System Composed of Triboelectric Nanogenerators and Supercapacitors

Triboelectric nanogenerators (TENG) are a possible power source for wearable electronics, but the conventional electrode materials for TENG are metals such as Cu and Al that are easy to be oxidized or corroded in some harsh environments. In this paper, metal electrode material is replaced by an electrical conducting polymer, polypyrrole (PPy), for the first time. Moreover, by utilizing PPy with micro/nanostructured surface as the triboelectric layer, the charge density generated is significantly improved, more superior to that of TENG with metals as the triboelectric layer. As this polymer‐based TENG is further integrated with PPy‐based supercapacitors, an all‐plastic‐materials based self‐charging power system is built to provide sustainable power with excellent long cycling life. Since the environmental friendly materials are adopted and the facile electrochemical deposition technique is applied, the new self‐charging power system can be a practical and low cost power solution for many applications.     

Triboelectric Nanogenerators as a Self‐Powered Motion Tracking System

Motion tracking is a key area of sensor systems for security, transportation, and high‐tech industry. In this work, a self‐powered motion tracking system is developed to monitor moving speed, direction, acceleration, starting and ending positions, and even the moving path of a moving object. Such a system is based on a set of triboelectric nanogenerators (TENGs) that are composed of two friction layers with opposite triboelectric polarities (Kapton and Aluminum) and operates in the sliding mode. Velocities of a moving object are monitored from ?0.1 m s^‐1 to +0.1 m s^‐1 at a step of 0.01 m s^‐1, and accelerations from ?0.1 m s^‐2 to +0.1 m s^‐2 at a step of 0.02 m s^‐2. Furthermore, an 8 × 8 two‐dimensional coordinates system with 16 groups of TENGs is created, and the moving path of an object is obtained. This study opens up a new area of TENGs as active sensors with great potential in self‐powered systems, positioning detecting, motion tracking, environmental and infrastructure monitoring, and security.     

Single‐Thread‐Based Wearable and Highly Stretchable Triboelectric Nanogenerators and Their Applications in Cloth‐Based Self‐Powered Human‐Interactive and Biomedical Sensing

The development of wearable and large‐area fabric energy harvester and sensor has received great attention due to their promising applications in next‐generation autonomous and wearable healthcare technologies. Here, a new type of “single” thread‐based triboelectric nanogenerator (TENG) and its uses in elastically textile‐based energy harvesting and sensing have been demonstrated. The energy‐harvesting thread composed by one silicone‐rubber‐coated stainless‐steel thread can extract energy during contact with skin. With sewing the energy‐harvesting thread into a serpentine shape on an elastic textile, a highly stretchable and scalable TENG textile is realized to scavenge various kinds of human‐motion energy. The collected energy is capable to sustainably power a commercial smart watch. Moreover, the simplified single triboelectric thread can be applied in a wide range of thread‐based self‐powered and active sensing uses, including gesture sensing, human‐interactive interfaces, and human physiological signal monitoring. After integration with microcontrollers, more complicated systems, such as wireless wearable keyboards and smart beds, are demonstrated. These results show that the newly designed single‐thread‐based TENG, with the advantage of interactive, responsive, sewable, and conformal features, can meet application needs of a vast variety of fields, ranging from wearable and stretchable energy harvesters to smart cloth‐based articles.     

Stretchable,Transparent, and Thermally Stable Triboelectric Nanogenerators Based on Solvent‐Free Ion‐Conducting Elastomer Electrodes

The development of stretchable/soft electronics requires power sources that can match their stretchability. In this study, a highly stretchable, transparent, and environmentally stable triboelectric nanogenerator with ionic conductor electrodes (iTENG) is reported. The ion‐conducting elastomer (ICE) electrode, together with a dielectric elastomer electrification layer, allows the ICE‐iTENG to achieve a stretchability of 1036% and transmittance of 91.5%. Most importantly, the ICE is liquid solvent‐free and thermally stable up to 335 °C, avoiding the dehydration‐induced performance degradation of commonly used hydrogels. The ICE‐iTENG shows no decrease in electrical output even after storing at 100 °C for 15 h. Biomechanical motion energies are demonstrated to be harvested by the ICE‐iTENG for powering wearable electronics intermittently without extra power sources. An ICE‐iTENG‐based pressure sensor is also developed with sensitivity up to 2.87 kPa^?1. The stretchable ICE‐iTENG overcomes the strain‐induced performance degradation using percolated electrical conductors and liquid evaporation‐induced degradation using ion‐conducting hydrogels/ionogels, suggesting great promising applications in soft/stretchable electronics under a relatively wider temperature range.     

MoSe2 Enhanced Raindrop Triboelectric Nanogenerators and Its Energy Conversion Analysis

Triboelectric nanogenerators (TENGs) are considered one of the most effective methods for harvesting irregular and low-frequency raindrop energy. In this work, molybdenum selenide (MoSe₂) nanosheets act as intermediate layers for improving droplet-based TENG performance. Consequently, without surface etching process, the short-circuit current (I_sc) and open-circuit voltage (V_oc) of the TENG can reach as high as 1.2 mA and 120 V, respectively. Furthermore, precise energy analysis based on an optimization model for input energy calculation is carried out, allowing conversion efficiency to be calculated under diverse conditions. Finally, an all-solid supercapacitor is fabricated for integration with the TENG. An intelligent wireless sensing system, powered by the integrated TENG and capacitor, is demonstrated for monitoring environmental information. This study provides new insights into intermediate-layer materials' selection and action mechanisms. It fills a gap in the research on a precise model of theoretical energy conversion efficiency calculation. The integrated devices and sensing applications will provide strategies for creating smart cities.